The present invention relates to a method for determination of fluorescent products in polymerization reactions. In particular, the invention relates to a method for rapid measurement of fluorescent products in solid and solution polycarbonate samples to provide information about the samples"" composition or physical properties.
Aromatic polycarbonates are typically synthesized by reaction of an aromatic diphenol, such as 2,2xe2x80x2-bis(4-hydroxyphenyl)propane (also known as bisphenol A or BPA), with derivatives of carbonic acid, such as phosgene or diphenyl carbonate, in the presence of a catalyst. See, for example, U.S. Pat. No. 3,028,365 to Schnell et al., U.S. Pat. No. 3,334,154 to Kim, U.S. Pat. No. 3,989,672 to Vestergaard, U.S. Pat. No. 4,131,575 to Adelmann et al., and U.S. Pat. No. 5,606,008 to Sakashita et al.; World Patent Application 1999-50335 to Funakoshi et al.; and Japanese Unexamined Patent Publications JP 2000-063507-A, JP 11-005837-A and JP 11-158261-A.
One important property of the synthetic reaction conditions is selectivity for the formation of linear versus branched polycarbonate chains. Product selectivity may be defined as the ratio of the molecular weight (number average molecular weight, Mn, or weight average molecular weight, Mw) of polycarbonate to the concentration of branched product, also known as Fries product. Formation of Fries product, shown schematically below, can occur through selective catalysis or rearrangement to form a branched polycarbonate. 
The phenyl salicylate product II and the branched polycarbonate III are collectively referred to herein as Fries product. The properties of the product polycarbonate are strongly influenced by the amount of Fries product present, and it is often desirable to minimize the Fries product content for consistent melt flow properties. Therefore, in exploring new reaction conditions for polycarbonate synthesis, it would be useful to employ a rapid and convenient technique for characterizing product selectivity.
Traditional techniques for measurements of polymer molecular weight, such as size-exclusion chromatography and light scattering, require extensive and time-consuming sample preparation steps to dissolve the solid polymer for analysis. See, for example, the techniques described by G. C. Berry in Concise Encyclopedia of Materials Characterization, R. W. Cahn and E. Lifshin, eds., Pergamon Press, Oxford England, pages 343-350 (1993); H. G. Barth, Advances in Chemistry Series, volume 247, pages 3-11 (1995); and K. Reihs, M. Voetz, M. Kruft, D. Wolany, and A. Benninghoven, Fresnius"" Journal of Analytical Chemistry, volume 358, pages 93-95 (1997). Similar time-consuming sample preparation is also needed for measurements of Fries product by traditional techniques such as nuclear magnetic resonance (NMR) spectroscopy and high performance liquid chromatography (HPLC). See, for example, A. Factor, xe2x80x9cMechanisms of Thermal and Photodegradation of Bisphenyl A Polycarbonatexe2x80x9d, Chapter 5 in R. L. Clough et al. eds., xe2x80x9cPolymer Durability:
Degradation, Stabilization, and Lifetime Predictionxe2x80x9d, 1995, American Chemical Society. Thus, molecular weight and Fries analysis by means of known techniques is both time and labor intensive. In addition, these techniques are invasive and destructive of sample.
There accordingly remains a need in the art for a method to rapidly characterize aromatic polycarbonates and thus the product selectivity of reaction conditions. There also remains a need for a method of monitoring product selectivity that is non-destructive and sufficiently rapid to monitor the progress of polycarbonate synthesis reactions in situ.
A rapid and convenient method for characterizing an aromatic polycarbonate comprises: providing at least one analytical sample comprising an aromatic polycarbonate; irradiating the analytical sample at a first wavelength range to excite fluorescence; detecting fluorescence emission intensities from the analytical sample at least a second wavelength range and a third wavelength range, the second wavelength range and the third wavelength range being separated from each other and from the first wavelength range by at least five nanometers; and characterizing the analytical sample based on the fluorescence emission intensities at the second wavelength range and the third wavelength range.